Flickering faces in Edit mode 2.83
I had the exact same behavior and it came out of nowhere.

Pixelated diagonals over faces
Faces flickering from gray to orange when selected
Strange see-through

I already worked in the same version of Blender (2.83.0) before on the same computer without this problem.
Solved it by uninstalling Blender and reinstalling version 2.83.2